Etching method and apparatus

ABSTRACT

An etching apparatus comprises a workpiece holder ( 21 ) for holding a workpiece (X), a plasma generator ( 10, 20 ) for generating a plasma ( 30 ) in a vacuum chamber ( 3 ), an orifice electrode ( 4 ) disposed between the workpiece holder ( 21 ) and the plasma generator ( 10, 20 ), and a grid electrode ( 5 ) disposed upstream of the orifice electrode ( 4 ) in the vacuum chamber ( 3 ). The orifice electrode ( 4 ) has orifices ( 4   a ) defined therein. The etching apparatus further comprises a voltage applying unit ( 25, 26 ) for applying a voltage between the orifice electrode ( 4 ) and the grid electrode ( 5 ) to accelerate ions from the plasma ( 30 ) generated by the plasma generator ( 10, 20 ) and to pass the extracted ions through the orifices ( 4   a ) in the orifice electrode ( 4 ). A first collimated neutral particle beam is generated and applied to the workpiece (X) for etching a surface of a processing layer ( 60 ) of the workpiece (X). A second collimated neutral particle beam is generated, and a mask ( 50 ) for covering at least a portion of the surface of the processing layer ( 60 ) is sputtered by the second neutral particle beam to form a protecting film ( 80 ) on a sidewall ( 60   a ) of the processing layer ( 60 ) for protecting the sidewall ( 60   a ) of the processing layer ( 60 ) from being etched by the first neutral particle beam.

TECHNICAL FIELD

[0001] The present invention relates to an etching method and apparatussuitable for use in micromachining processes involved in the fabricationof semiconductor devices or the like, and more particularly to anetching method and apparatus for processing a surface of a workpiecewith use of a neutral particle beam generated by neutralizing positiveor negative ions generated in a plasma.

BACKGROUND ART

[0002] In recent years, semiconductor integrated circuits,micromachines, and the like have been processed in highly fine patterns.Therefore, a highly accurate process with a high selectivity and aprocess to form a high aspect ratio pattern are required. In the fieldsof such processing, there has widely been used a plasma etchingapparatus.

[0003] As a plasma etching apparatus, there has been known a reactiveion etching (RIE) apparatus which generates various kinds of particlesincluding positive ions and radicals. The positive ions or the radicalsare applied to a workpiece to etch the workpiece.

[0004] In an etching process utilizing such an RIE apparatus, there havebeen problems that high accuracy and high selectivity cannot be achievedsimultaneously and etching profile irregularities are caused by chargebuild-up. The selectivity is a ratio of the etched depth in a workpieceto the etched depth in a mask or an underlying material. Specifically,when a workpiece is etched by x μm and a mask protecting the workpieceis etched by y μm, the selectivity s is expressed by s=x/y. In the caseof a higher selectivity, the mask is less damaged and the workpiece canbe etched to form a pattern having a high aspect ratio.

[0005] In order to enhance the selectivity, a combination of gases whichcan deposit on the mask or the underlying material but can etch theworkpiece has been used in the conventional etching process. Further,radicals deposit onto the sidewall surface of the workpiece to form asidewall passivation layer. If the sidewall passivation layer isexcessively formed on the surface of the workpiece, then the surface ofthe workpiece is processed into a tapered shape, so that dimensionalaccuracy is lowered in the etching process. When a combination of Cl₂gas and O₂ gas is used in the conventional etching process, theselectivity of Si/SiO₂ is at most about 100. Thus, this combination ofgases can achieve a higher selectivity than other combinations of gases.However, devices having a pattern smaller than 0.1 μm have been requiredto be processed with high accuracy and a selectivity higher than 300.Particularly, it will be the future task to simultaneously achieve ahigher selectivity over an underlying layer of a gate oxide film and noresidue at step portions for isolation.

[0006] The etching profile irregularities are caused by the differencebetween the behavior of electrons and that of positive ions.Specifically, the etching profile irregularities, i.e., notches, areproduced at sidewalls defining stripes of a fine pattern. When theetching process is performed with a low energy ion beam, electrons aredecelerated within the fine pattern by a negative self-bias potential onthe workpiece, and trapped near a resist. On the other hand, ions areaccelerated and delivered to the underlying layer of the oxide film todevelop positive charge build-up on the workpiece. However, at theoutside of the fine pattern, charge build-up is not developed becausethe same amounts of electrons and ions are delivered thereto andneutralized. Thus, a potential difference is produced between the insideand outside of the fine pattern, so that the trajectories of the ionsare curved to produce the notches.

DISCLOSURE OF INVENTION

[0007] The present invention has been made in view of the abovedrawbacks. It is therefore an object of the present invention to providean etching method and apparatus which can etch a surface of a workpiecewithout charge build-up or etching profile irregularities on theworkpiece, and can simultaneously achieve high accuracy and highselectivity over a mask or an underlying layer for a fine pattern.

[0008] According to a first aspect of the present invention, there isprovided an etching method comprising: etching a surface of a processinglayer of a workpiece by generating a first collimated neutral particlebeam from a first gas and applying the first neutral particle beam tothe workpiece; and forming a protecting film on a sidewall of theprocessing layer for protecting the sidewall of the processing layerfrom being etched by the first neutral particle beam. The first neutralparticle beam should preferably have an energy ranging from 10 eV to 50eV.

[0009] According to the present invention, in the etching process, thesurface of the processing layer is etched by the first neutral particlebeam having no electric charges but having a large translational energyranging from 10 eV to 50 eV. Therefore, secondary electrons are notemitted from the surface of the processing layer, and hence theworkpiece can be etched with a lower charge build-up voltage. Further,since the collimated neutral particle beam is applied to the workpiece,the workpiece can highly accurately be etched even in the case where asidewall passivation layer is not formed on the surface of theprocessing layer. Specifically, the processing layer is hardly sputteredby the neutral particle beam having a low energy ranging form 10 eV to50 eV, and thermochemical reaction occurs between the neutral particlebeam and the processing layer. As a result, a reaction product isspontaneously sublimed on the processing layer to perform the etchingprocess. If the neutral particles have no directionality and executethermal motion, then the workpiece is isotropically etched. However,according to the present invention, since the neutral particle beam iscollimated, anisotropic etching can be achieved. When the neutralparticle beam has an energy ranging from 10 eV to 50 eV, a resist ishardly sputtered by the neutral particle beam. Therefore, the workpiececan be etched with high selectivity.

[0010] When an ion beam having a low energy is applied to the workpiecein a conventional RIE apparatus, the ion beam may be curved due to anelectric field produced by charge unbalance between ions and electronswithin a fine pattern, so that notches may be produced as local etchingprofile irregularities. According to the present invention, however,since the etching method utilizes a neutral particle beam, it ispossible to etch the workpiece to form a pattern having a high aspectratio without generating notches.

[0011] In the forming process, the protecting film can be formed on thesidewall of the processing layer for protecting the sidewall of theprocessing layer from being etched by the first neutral particle beam.Therefore, a highly accurate etching process can be achieved in such astate that the sidewall of the processing layer is prevented from beingetched by the first neutral particle beam. Thus, the etching methodaccording to the present invention can simultaneously achieve highaccuracy and high selectivity for a fine pattern.

[0012] According to a preferred aspect of the present invention, theetching method further comprises covering at least a portion of thesurface of the processing layer with a shielding member, the formingcomprising: generating a second collimated neutral particle beam fromthe first gas; and sputtering the shielding member by the second neutralparticle beam to form the protecting film on the sidewall of theprocessing layer. The second neutral particle beam should preferablyhave an energy ranging from 50 eV to 200 eV.

[0013] According to a preferred aspect of the present invention, theforming comprises: generating a second collimated neutral particle beamfrom a second gas; and applying the second neutral particle beam to thesurface of the processing layer to form the protecting film on thesidewall of the processing layer.

[0014] According to a preferred aspect of the present invention, theprocessing layer comprises a silicon layer, the first gas includes SF₆,and the second gas includes a fluorocarbon gas.

[0015] According to a preferred aspect of the present invention, theprocessing layer comprises a silicon layer, and a layer underlying theprocessing layer comprises a silicon oxide film; wherein the forming isperformed immediately before the etching is completed, and then theetching is performed again.

[0016] Thus, the present invention is suitable for use in a gate etchingprocess in which the processing layer comprises a silicon layer and alayer underlying the processing layer comprises a silicon oxide film.According to the present invention, a gate etching process with a highselectivity can be performed without any residues or any damages on theworkpiece.

[0017] According to a preferred aspect of the present invention, theetching method further comprises removing the protecting film formed onthe sidewall of the processing layer.

[0018] According to a preferred aspect of the present invention, theetching method further comprises repeating the etching, the removing,and the forming.

[0019] According to a second aspect of the present invention, there isprovided an etching apparatus comprising: a workpiece holder for holdinga workpiece; a plasma generator for generating a plasma in a vacuumchamber; a first electrode disposed between the workpiece holder and theplasma generator, the first electrode having orifices defined therein; asecond electrode disposed upstream of the first electrode in the vacuumchamber; and a voltage applying unit for applying a voltage between thefirst electrode and the second electrode to accelerate ions from theplasma generated by the plasma generator and to pass the extracted ionsthrough the orifices in the first electrode; wherein a first collimatedneutral particle beam is generated and applied to the workpiece foretching a surface of a processing layer of the workpiece; wherein asecond collimated neutral particle beam is generated, and a shieldingmember for covering at least a portion of the surface of the processinglayer is sputtered by the second neutral particle beam to form aprotecting film on a sidewall of the processing layer for protecting thesidewall of the processing layer from being etched by the first neutralparticle beam. The first neutral particle beam should preferably have anenergy ranging from 10 eV to 50 eV. The second neutral particle beamshould preferably have an energy ranging from 50 eV to 200 eV.

[0020] According to a preferred aspect of the present invention, theetching apparatus further comprises an end point detector for detectingan end point of an etching process.

[0021] According to a third aspect of the present invention, there isprovided an etching apparatus comprising: a workpiece holder for holdinga workpiece; a plasma generator for generating a plasma in a vacuumchamber; a first electrode disposed between the workpiece holder and theplasma generator, the first electrode having orifices defined therein; asecond electrode disposed upstream of the first electrode in the vacuumchamber; and a voltage applying unit for applying a voltage between thefirst electrode and the second electrode to accelerate ions from theplasma generated by the plasma generator and to pass the extracted ionsthrough the orifices in the first electrode; wherein a first collimatedneutral particle beam is generated and applied to the workpiece foretching a surface of a processing layer of the workpiece; wherein asecond collimated neutral particle beam is generated, and the firstelectrode is sputtered by the second neutral particle beam to form aprotecting film on a sidewall of the processing layer for protecting thesidewall of the processing layer from being etched by the first neutralparticle beam. The first neutral particle beam should preferably have anenergy ranging from 10 eV to 50 eV. The second neutral particle beamshould preferably have an energy ranging from 50 eV to 200 eV.

[0022] According to a preferred aspect of the present invention, theetching apparatus further comprises an end point detector for detectingan end point of an etching process.

BRIEF DESCRIPTION OF DRAWINGS

[0023]FIG. 1 is a schematic view showing a whole arrangement of anetching apparatus according to a first embodiment of the presentinvention;

[0024]FIG. 2A is a perspective view showing an orifice electrode in theetching apparatus shown in FIG. 1;

[0025]FIG. 2B is a vertical cross-sectional view partially showing theorifice electrode shown in FIG. 2A;

[0026]FIGS. 3A and 3B are schematic views showing an etching process inthe etching apparatus shown in FIG. 1;

[0027]FIGS. 4A and 4B are schematic views showing an example of anetching process; and

[0028]FIG. 5 is a schematic view showing a whole arrangement of anetching apparatus according to a second embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0029] An etching apparatus according to embodiments of the presentinvention will be described in detail below with reference to FIGS. 1through 5. Like or corresponding components are denoted by like orcorresponding reference numerals throughout drawings, and will not bedescribed below repetitively.

[0030]FIG. 1 is a schematic view showing a whole arrangement of anetching apparatus according to a first embodiment of the presentinvention, with electric components in block form. As shown in FIG. 1,the etching apparatus comprises a cylindrical vacuum chamber 3constituted by a beam generating chamber 1 for generating a neutralparticle beam and a process chamber 2 housing therein a workpiece X suchas a semiconductor substrate, a glass workpiece, an organic workpiece,or a ceramic workpiece. The beam generating chamber 1 of the vacuumchamber 3 has walls made of quartz glass or ceramics, and the processchamber 2 of the vacuum chamber 3 has walls made of metal.

[0031] The beam generating chamber 1 has a coil 10 disposed therearoundfor inductively coupled plasma (ICP). The coil 10 is housed in awater-cooled tube having an outside diameter of about 8 mm, for example.The coil 10 of about two turns is wound around the beam generatingchamber 1. The coil 10 is electrically connected to a high-frequencypower supply 20, which applies a high-frequency voltage having afrequency of about 13.56 MHz, for example, to the coil 10. When ahigh-frequency current is supplied from the high-frequency power supply20 to the coil 10, an induced magnetic field is produced in the beamgenerating chamber 1 by the coil 10. The varying magnetic field inducesan electric field, which accelerates electrons to generate a plasma 30in the beam generating chamber 1. Thus, the coil 10 and thehigh-frequency power supply 20 constitute a plasma generator forgenerating a plasma 30 in the beam generating chamber 1.

[0032] The beam generating chamber 1 has a gas inlet port 11 defined inan upper portion thereof for introducing a gas into the beam generatingchamber 1. The gas inlet port 11 is connected through a gas supply pipe12 to a gas supply source 13, which supplies a gas such as SF₆, CHF₃,CF₄, Cl₂, Ar, O₂, N₂, C₄F₈, CF₃I, and C₂F₄ to the beam generatingchamber 1.

[0033] The process chamber 2 houses a workpiece holder 21 therein forholding the workpiece X. The workpiece X is placed on an upper surfaceof the workpiece holder 21. The process chamber 2 has a gas outlet port22 defined in a sidewall thereof for discharging the gas from theprocess chamber 2. The gas outlet port 22 is connected through a gasoutlet pipe 23 to a vacuum pump 24, which operates to maintain theprocess chamber 2 at a predetermined pressure.

[0034] The process chamber 2 has an end point detector 40 provided atthe sidewall thereof for monitoring the etching process and detecting anend point of the etching process. The end point detector 40 may comprisea quadrupole mass spectrometer, for example. Alternatively, the endpoint detector 40 may utilize laser interference or ellipsometry todetect an end point of the etching process.

[0035] An orifice plate (orifice electrode) 4 made of an electricallyconductive material such as graphite is disposed as a first electrode inthe lower end of the beam generating chamber 1. The orifice electrode 4is electrically connected to a DC power supply 25. FIG. 2A is aperspective view showing the orifice electrode 4, and FIG. 2B is avertical cross-sectional view partially showing the orifice electrode 4shown in FIG. 2A. As shown in FIGS. 2A and 2B, the orifice electrode 4has a number of orifices 4 a defined therein. Typically, the orificeelectrode 4 has a number of orifices 4 a each having a diameter of 1 mmand a length of 10 mm, and the orifices 4 a are arranged with a pitch of1.4 mm. The beam generating chamber 1 is separated from the processchamber 2 by the orifice plate 4. Therefore, the pressure of the processchamber 2 can be set to be lower than that of the beam generatingchamber 1 with the vacuum pump 24.

[0036] An electrode 5 made of an electrically conductive material isdisposed as a second electrode in the upper end of the beam generatingchamber 1. The electrode 5 is electrically connected to a DC powersupply 26. The electrode 5 may comprise a plate made of metal, silicon,or graphite and having no holes. Alternatively, the electrode 5 maycomprise a plate having a number of holes defined therein forintroducing the gas uniformly into the beam generating chamber 1. The DCpower supply 25 and the DC power supply 26 constitute a voltage applyingunit for applying a voltage between the orifice electrode 4 and theelectrode 5.

[0037] Operation of the etching apparatus according to the presentembodiment will be described below. In the present embodiment, anetching process (gate etching process) of etching a polycrystallinesilicon layer formed on a silicon oxide film of a semiconductorsubstrate will be described as an example.

[0038] The vacuum pump 24 is driven to evacuate the vacuum chamber 3,and then a gas such as SF₆ is introduced from the gas supply source 13into the beam generating chamber 1. For example, the pressure in thebeam generating chamber 1 is set to be 0.1 Pa, and the pressure in theprocessing chamber 2 is set to be 1 Pa. A high-frequency voltage havinga frequency of about 13.56 MHz is applied to the coil 10 for 50microseconds by the high-frequency power supply 20, so that ahigh-frequency electric field is produced in the beam generating chamber1. The gas introduced into the beam generating chamber 1 is ionized byelectrons that are accelerated by the high-frequency electric field, forthereby generating a high-density plasma 30 in the beam generatingchamber 1. The plasma 30 is mainly composed of positive ions and heatedelectrons.

[0039] Then, the high-frequency voltage applied by the high-frequencypower supply 20 is interrupted for 50 microseconds. As a result, theelectron temperature is lowered by inelastic collision of the electrons,and the electrons are attached to the residual process gas to generatenegative ions. Thereafter, the high-frequency voltage is applied againto the coil 10 for 50 microseconds by the high-frequency power supply 20to heat the electrons in the plasma in the beam generating chamber 1.Thus, the above cycle is repeated. In this manner, the application ofthe high-frequency voltage for 50 microseconds and the interruption ofthe high-frequency voltage for 50 microseconds are alternately repeated.The period of time (50 microseconds) for which the high-frequencyvoltage is interrupted is sufficiently longer than a period of time inwhich the electrons in the plasma 30 are attached to the residualprocess gas to generate negative ions, and sufficiently shorter than aperiod of time in which the electron density in the plasma 30 is loweredto extinguish the plasma. The period of time (50 microseconds) for whichthe high-frequency voltage is applied is long enough to recover theenergy of the electrons in the plasma 30 which has been lowered duringthe interruption of the high-frequency voltage.

[0040] While ordinary plasmas are mostly composed of positive ions andelectrons, the etching apparatus according to the present embodiment canefficiently generate a plasma in which positive ions and negative ionscoexist therein. Although the high-frequency voltage is interrupted for50 microseconds in the above example, it may be interrupted for a periodof time ranging from 50 to 100 microseconds to generate a large quantityof negative ions as well as positive ions in the plasma.

[0041] The DC power supply 25 applies a voltage of −50 V to the orificeplate 4, and the DC power supply 26 applies a voltage −100 V to theelectrode 5. Accordingly, a potential difference is produced between theorifice electrode 4 and the electrode 5. Therefore, as shown in FIG. 2B,the negative ions 6 generated in the beam generating chamber 1 areaccelerated toward the orifice electrode 4 by the potential differenceand introduced into the orifices 4 a defined in the orifice electrode 4.Most of the negative ions 6 that are passing through the orifices 4 a inthe orifice electrode 4 are collided with the sidewall surfaces of theorifices 4 a and hence neutralized in the vicinity of solid sidewallsurfaces of the orifices 4 a, or are collided with gas moleculesremaining within the orifices 4 a and hence neutralized by chargeexchange with the gas molecules. Thus, the negative ions are convertedinto neutral particles (fluorine atoms) 7.

[0042] The orifice electrode 4 serves not only to neutralize the ions,but also to collimate the neutral particle beam and further to separatethe beam generating chamber 1 and the process chamber 2 from each other.The workpiece can highly accurately be etched with the collimatedneutral particle beam. Since the beam generating chamber 1 and theprocess chamber 2 are separated from each other, the pressure of theprocess chamber 2 can be set to be lower than the pressure of the beamgenerating chamber 1, so that the accurate etching can be achieved.Further, the orifice electrode 4 which separates the beam generatingchamber 1 and the process chamber 2 from each other can prevent aradiation produced by the plasma from being applied to the workpiece X.Specifically, since the beam generating chamber 1 where the plasma isgenerated is isolated from the workpiece X by the orifice electrode 4,the radiation produced by the plasma is not substantially applied to theworkpiece X. Therefore, it is possible to reduce adverse effects on theworkpiece X due to the radiation such as an ultraviolet ray which wouldotherwise damage the workpiece X.

[0043] As described above, the negative ions that have been neutralizedwhen passing through the orifices 4 a, i.e., fluorine atoms, are emittedas an energetic beam having a low energy into the process chamber 2. Thefluorine atoms travel directly in the process chamber 2 and are appliedto the workpiece (semiconductor substrate) X placed on the workpieceholder 21. As shown in FIG. 3A, the fluorine atoms applied to theworkpiece X are spontaneously sublimed as SiF₄ on the processing layer(polycrystalline silicon layer) 60 of the workpiece X according to thefollowing thermochemical equation.

Si+4F→SiF₄↑

[0044] Thus, the etching process is performed at portions of thepolycrystalline silicon layer 60 which are not covered with a mask 50.As shown in FIG. 3A, the etching portion has a sidewall 60 a formed inthe polycrystalline silicon layer 60. Although the mask 50 is a resistmade of organic matter, the mask 50 is not sputtered by the beam becausethe beam has a low energy. The beam for etching the polycrystallinesilicon layer 60, i.e., a first neutral particle beam, should preferablyhave an energy ranging from 10 eV to 50 eV.

[0045] In this etching process, the end point detector 40 detects an endpoint of the process. When the end point detector 40 detects an endpoint of the etching process (immediately before or immediately afterthe silicon oxide film 70 is exposed), the DC power supply 25 changesthe voltage to be applied to the orifice electrode 4 from −50 V to +100V, for example. The change of the voltage applied to the orificeelectrode 4 increases the energy of the beam emitted into the processchamber 2. Therefore, the mask 50 made of organic matter is sputtered bythe beam having an increased energy, for thereby forming an organic film80 of CH_(x)F_(y) on the sidewall 60 a of the polycrystalline siliconlayer 60 as shown in FIG. 3B. Thus, the sidewall 60 a of thepolycrystalline silicon layer 60 is covered with the organic film 80.The organic film 80 serves as a protecting film for protecting thesidewall 60 a of the polycrystalline silicon layer 60 from being etchedby the fluorine atoms. The beam for forming the protecting film 80,i.e., a second neutral particle beam, should preferably have an energyranging from 50 eV to 200 eV.

[0046] After the organic film 80 having a predetermined thickness isdeposited on the sidewall 60 a of the polycrystalline silicon layer 60,the DC power supply 25 changes the voltage to be applied to the orificeplate 4 from +100 V to −50 V. As a result, an energetic beam (the firstneutral particle beam) having a low energy and a high reactivity isemitted again into the process chamber 2. Since the protecting film 80has been deposited on the sidewall 60 a of the polycrystalline siliconlayer 60, the sidewall 60 a of the polycrystalline silicon layer 60 isnot etched by the beam. Therefore, the highly accurate etching processcan be achieved. Since the etching process in the present embodimentutilizes F radicals which are more reactive than Cl radicals or Brradicals, the etching rate can be increased.

[0047] As shown in FIG. 4A, in the case of an etching process (gateetching process) of etching a polycrystalline silicon layer 110 formedon an underlying silicon oxide film 100 with use of a collimatedfluorine neutral particle beam having an energy ranging from 10 eV to 50eV, the polycrystalline silicon layer 110 is etched in a verticaldirection according to the following thermochemical equation.

Si+4F→SiF₄↑

[0048] Since the silicon oxide film 100 does not react with the fluorineatoms, even if the etching process is performed until the silicon oxidefilm 100 is exposed, the silicon oxide film 100 is not etched by thebeam. Therefore, the workpiece X can be etched with a high selectivityof Si/SiO₂. In this case, however, the sidewall 110 a of thepolycrystalline silicon layer 110 may be etched by the fluorine atomsreflected on the surface 100 a of the silicon oxide film 100, resultingin etching profile irregularities, as shown in FIG. 4B. According to thepresent embodiment, as shown in FIG. 3B, the mask 50 is sputtered toform the protecting film 80 on the sidewall 60 a of the polycrystallinesilicon layer 60 for protecting the sidewall 60 a of the polycrystallinesilicon layer 60 from being etched by the fluorine neutral particlebeam. Therefore, according to the present embodiment, it is possible toprevent the aforementioned etching profile irregularities from beingcaused by the fluorine neutral particle beam.

[0049] In the present embodiment, the mask 50 is sputtered to form theprotecting film 80 on the sidewall 60 a of the polycrystalline siliconlayer 60. Instead of the mask 50, other shielding members may be usedfor covering at least a portion of the surface of the processing layer.For example, an orifice electrode 4 made of graphite is sputtered togenerate a CF_(x) beam, for thereby forming the protecting film on thesidewall of the processing layer. Alternatively, a meshed shieldingplate made of organic matter may be inserted between the orificeelectrode 4 and the workpiece X, and the shielding plate may besputtered to form the protecting film on the sidewall of the processinglayer.

[0050]FIG. 5 is a schematic view showing a whole arrangement of anetching apparatus according to a second embodiment of the presentinvention, with electric components in block form. As shown in FIG. 5, agas inlet port 11 is connected through two branched gas supply pipes 12a, 12 b to gas supply sources 13 a, 13 b. The gas supply source 13 asupplies a first gas such as SF₆ to the beam generating chamber 1, andthe gas supply source 13 b supplies a second gas such as a fluorocarbon(C₄F₈, CHF₃, C₂F₄, or the like) to the beam generating chamber 1. Thegas supply pipes 12 a, 12 b have valves 15 a, 15 b provided thereon,respectively.

[0051] Operation of the etching apparatus according to the presentembodiment will be described below. First, the valve 15 b of the gassupply pipe 12 b is closed, and the valve 15 a of the gas supply pipe 12a is opened. As a result, an etching gas such as SF₆ is introduced fromthe gas supply source 13 a into the beam generating chamber 1. As withthe first embodiment, a first neutral particle beam (fluorine atom beam)is generated from the plasma 30 in the beam generating chamber 1 andemitted into the processing chamber 2. Portions of a polycrystallinesilicon layer which are not covered with a mask are etched by theneutral particle beam having a low energy ranging from 10 eV to 50 eV.

[0052] When an end point of the etching process is detected by the endpoint detector 40, the valve 15 a of the gas supply pipe 12 a is closedand the valve 15 b of the gas supply pipe 12 b is opened. As a result, agas such as C₄F₈, CHF₃, or C₂F, is introduced from the gas supply source13 b into the beam generating chamber 1. Positive ions (CF_(x) ⁺ suchCF₂ ⁺, CF⁺, or CF₃ ⁺) are generated from the plasma 30 in the beamgenerating chamber 1. The positive ions are accelerated and neutralizedto generate a second neutral particle beam. The neutral particle beam isemitted into the processing chamber 2, for thereby forming a polymericfilm of CF, on a sidewall of the polycrystalline silicon layer. Thus,the sidewall of the polycrystalline silicon layer is covered with thepolymeric film. The polymeric film serves as a protecting film forprotecting the sidewall of the polycrystalline silicon layer from beingetched by the fluorine atoms as with the organic film 80 in the firstembodiment.

[0053] After the protecting film having a predetermined thickness isdeposited on the sidewall of the polycrystalline silicon layer, thevalve 15 b of the gas supply pipe 12 b is closed and the valve 15 a ofthe gas supply pipe 12 a is opened. As a result, the etching gas isintroduced into the beam generating chamber 1, and hence the firstneutral particle beam (fluorine atom beam) is emitted into theprocessing chamber 2. Since the protecting film of CF_(x) has beendeposited on the sidewall of the polycrystalline silicon layer, thesidewall of the polycrystalline silicon layer are not etched by thebeam. Therefore, the highly accurate etching process can be achieved.

[0054] In the first and second embodiment described above, the etchingprocess of the processing layer and the forming process of theprotecting film may be repeated. In this case, the protecting film isnot necessarily completely removed by the etching process, and hence theresidual protecting film may be formed into a tapered shape. In order toprevent the protecting film from having a tapered shape, the protectingfilm may be removed from the sidewall of the processing layer after theetching process of the processing layer before the forming process ofthe protecting film. For example, if a TEOS film is used as a mask andO₂ gas is introduced into the processing chamber 2, then the protectingfilm can be ashed by O₂ radicals. Thus, the protecting film can beremoved from the sidewall of the processing layer without etching themask or the processing layer.

[0055] Some charged particles may pass through the orifices 4 a in theorifice electrode 4. In order to prevent such charged particles frombeing applied to the workpiece X, a deflector or an electron trap may bedisposed downstream of the orifice electrode 4. A voltage is applied tothe deflector in a direction perpendicular to a beam traveling directionto change the traveling direction of charged particles, for therebypreventing the charged particles from being applied to the workpiece X.The electron trap produces a magnetic field of about 100 gauss in adirection perpendicular to a beam traveling direction to change thetraveling direction of electrons, for thereby preventing the electronsfrom being applied to the workpiece X.

[0056] As well known in the art, when an insulated workpiece such as aworkpiece made of glass or ceramics is processed, charge build-up may bedeveloped on the surface of the insulated workpiece. However, byapplying neutralized particles to the insulated workpiece as describedabove, various processes including an etching process and a depositionprocess can highly accurately be performed on the insulated workpiecewith a low charge build-up voltage being maintained. Various types ofgases may be introduced into the beam generating chamber 1 according tothe type of process to be performed on the workpiece X. For example, ina dry etching process, oxygen or a halogen gas may selectively be usedaccording to the kind of the workpiece X.

[0057] In the above embodiment, the plasma is generated with use of acoil for ICP. However, the plasma may be generated with use of anelectron cyclotron resonance source (ECR source), a coil for heliconwave plasma, a microwave, or the like. The frequency of thehigh-frequency voltage is not limited to 13.56 MHz, but may be in therange from 1 MHz to 20 GHz. The voltages applied to the orificeelectrode 4 and the electrode 5 are not limited to the above examples.

[0058] Although certain preferred embodiments of the present inventionhave been shown and described in detail, it should be understood thatvarious changes and modifications may be made therein without departingfrom the scope of the appended claims.

INDUSTRIAL APPLICABILITY

[0059] The present invention is applicable to an etching method andapparatus suitable for use in micromachining processes involved in thefabrication of semiconductor devices or the like.

1. An etching method comprising: etching a surface of a processing layerof a workpiece by generating a first collimated neutral particle beamfrom a first gas and applying said first neutral particle beam to theworkpiece; and forming a protecting film on a sidewall of saidprocessing layer by a second collimated neutral particle beam to protectthe sidewall of said processing layer from being etched by said firstneutral particle beam.
 2. An etching method according to claim 1,wherein said first neutral particle beam has an energy ranging from 10eV to 50 eV.
 3. An etching method according to claim 1, furthercomprising covering at least a portion of the surface of said processinglayer with a shielding member, said forming comprising: generating saidsecond collimated neutral particle beam from said first gas; andsputtering said shielding member by said second neutral particle beam toform the protecting film on the sidewall of said processing layer.
 4. Anetching method according to claim 3, wherein said second neutralparticle beam has an energy ranging from 50 eV to 200 eV.
 5. An etchingmethod according to claim 1, wherein said forming comprises: generatingsaid second collimated neutral particle beam from a second gas; andapplying said second neutral particle beam to the surface of saidprocessing layer to form the protecting film on the sidewall of saidprocessing layer.
 6. An etching method according to claim 5, whereinsaid processing layer comprises a silicon layer, said first gas includesSF₆, and said second gas includes a fluorocarbon gas.
 7. An etchingmethod according to claim 1, wherein said processing layer comprises asilicon layer, and a layer underlying said processing layer comprises asilicon oxide film; wherein said forming is performed immediately beforesaid etching is completed, and then said etching is performed again. 8.An etching method comprising: etching a surface of a processing layer ofa workpiece by generating a first collimated neutral particle beam froma first gas and applying said first neutral particle beam to theworkpiece; forming a protecting film on a sidewall of said processinglayer for protecting the sidewall of said processing layer from beingetched by said first neutral particle beam; and removing said protectingfilm formed on the sidewall of said processing layer.
 9. An etchingmethod according to claim 8, further comprising repeating said etching,said removing, and said forming.
 10. An etching apparatus comprising: aworkpiece holder for holding a workpiece; a plasma generator forgenerating a plasma in a vacuum chamber; a first electrode disposedbetween said workpiece holder and said plasma generator, said firstelectrode having orifices defined therein; a second electrode disposedupstream of said first electrode in said vacuum chamber; and a voltageapplying unit for applying a voltage between said first electrode andsaid second electrode to accelerate ions from the plasma generated bysaid plasma generator and to pass the extracted ions through saidorifices in said first electrode; wherein a first collimated neutralparticle beam is generated and applied to the workpiece for etching asurface of a processing layer of the workpiece; wherein a secondcollimated neutral particle beam is generated, and a shielding memberfor covering at least a portion of the surface of said processing layeris sputtered by said second neutral particle beam to form a protectingfilm on a sidewall of said processing layer for protecting the sidewallof said processing layer from being etched by said first neutralparticle beam.
 11. An etching apparatus according to claim 10, whereinsaid first neutral particle beam has an energy ranging from 10 eV to 50eV.
 12. An etching apparatus according to claim 10, wherein said secondneutral particle beam has an energy ranging from 50 eV to 200 eV.
 13. Anetching apparatus according to claim 10, further comprising an end pointdetector for detecting an end point of an etching process.
 14. Anetching apparatus comprising: a workpiece holder for holding aworkpiece; a plasma generator for generating a plasma in a vacuumchamber; a first electrode disposed between said workpiece holder andsaid plasma generator, said first electrode having orifices definedtherein; a second electrode disposed upstream of said first electrode insaid vacuum chamber; and a voltage applying unit for applying a voltagebetween said first electrode and said second electrode to accelerateions from the plasma generated by said plasma generator and to pass theextracted ions through said orifices in said-first electrode; wherein afirst collimated neutral particle beam is generated and applied to theworkpiece for etching a surface of a processing layer of the workpiece;wherein a second collimated neutral particle beam is generated, and saidfirst electrode is sputtered by said second neutral particle beam toform a protecting film on a sidewall of said processing layer forprotecting the sidewall of said processing layer from being etched bysaid first neutral particle beam.
 15. An etching apparatus according toclaim 14, wherein said first neutral particle beam has an energy rangingfrom 10 eV to 50 eV.
 16. An etching apparatus according to claim 14,wherein said second neutral particle beam has an energy ranging from 50eV to 200 eV.
 17. An etching apparatus according to claim 14, furthercomprising an end point detector for detecting an end point of anetching process.
 18. An etching method comprising: etching a surface ofa processing layer of a workpiece by generating a first collimatedneutral particle beam from a first gas and applying said first neutralparticle beam to the workpiece; and sputtering an electrode, which isused to generate a neutral particle beam, by a second collimated neutralparticle beam to form a protecting film on a sidewall of said processinglayer to protect the sidewall of said processing layer from being etchedby said first neutral particle beam.
 19. An etching method according toclaim 18, wherein said first neutral particle beam has an energy rangingfrom 10 eV to 50 eV.
 20. An etching method according to claim 18,wherein said second neutral particle beam has an energy ranging from 50eV to 200 eV.
 21. An etching method according to claim 18, wherein saidsecond neutral particle beam is generated from a second gas.
 22. Anetching method according to claim 21, wherein said processing layercomprises a silicon layer, said first gas includes SF6, and said secondgas includes a fluorocarbon gas.
 23. An etching method according toclaim 18, wherein said processing layer comprises a silicon layer, and alayer underlying said processing layer comprises a silicon oxide film;wherein said sputtering is performed immediately before said etching iscompleted, and then said etching is performed again.
 24. An etchingmethod according to claim 18, further comprising removing saidprotecting film formed on the sidewall of said processing layer.
 25. Anetching method according to claim 24, further comprising repeating saidetching, said removing, and said sputtering.